Imaging is an important tool used in the detection of a variety of biological molecules. For example, imaging devices may be used to detect and determine concentrations of molecules of a specific molecular weight, DNA, a specific DNA sequence, proteins, and carbohydrates. Typically the samples of interest are labeled using fluorescent dyes, radioisotopes, or enzyme activated light emitting (i.e., chemiluminescent) or fluorescent (i.e., chemifluorescent) chemicals.
UV, visible or IR light excites fluorescent dyes and markers. Once excited the dyes fluoresce, preferably emitting light at a wavelength distinguishable from the excitation wavelength. Radioactive and chemiluminescent signals are typically captured using either x-ray film or storage phosphor screens. The x-ray film is developed and read using a densitometer. The storage phosphor screen does not require development and is read out by scanning the screen with a beam of light. The readout beam produces an emission from the storage phosphor, the intensity of the emission being proportional to the original quantity of radiation retained by the storage phosphors.
A variety of devices have been described for use in detecting labeled biological samples. U.S. Pat. No. 3,746,840 discloses a device for high-resolution readout of information stored on a film. The device comprises a slit equal in width to the desired resolution with optical fibers behind the slit of a diameter equal to the slit width. The optical fibers collect the light as it crosses the slit and transmits it to the detectors.
U.S. Pat. No. 3,836,225 discloses a fiber optic laser scanner. The disclosed scanner uses two optical fiber sets attached to electromagnetic coils. The magnetic coils deflect the beam as required.
U.S. Pat. No. 3,892,468 discloses a passive array of variable length optical fibers that function as a dynamic scanner. Each consecutive fiber in the fiber array is incrementally longer than the preceding fiber. Thus light entering the fibers at the same time will exit the fibers at different times, the variations in exit times thus being correlated with different locations.
U.S. Pat. No. 4,877,966, discloses a device for measurement of low-level laser induced phosphorescence. The laser is directed through a beam expander and then aimed by mirrors. The induced phosphorescence is collected by a fiber optic face plate and passed to a photomultiplier tube.
U.S. Pat. No. 5,062,942 discloses a fluorescence detection system for use with electrophoresis gel plates. In the disclosed system the gel plate is illuminated with a laser excitation source and the emitted fluorescent light is separated into a plurality of virtual images that are subsequently passed through individual bandpass filters thereby providing multicolor fluorescence detection.
U.S. Pat. No. 5,290,419 discloses a multicolor fluorescence detection system utilizing multiple laser sources and means for detecting fluorescence as a function of wavelength. The individual laser sources are combined with a light chopper (e.g., rotary shutter) in order to irradiate the sample on a time-sharing basis.
U.S. Pat. No. 5,436,718 discloses a multi-function photometer for measuring the absorbance, fluorescence, and luminescence associated with a sample. The disclosed system uses optical fibers to transmit light to and from the sample using scanning head. A computer controlled positioning table is used to position the canning head with respect to the samples contained in a microplate.
U.S. Pat. No. 5,459,325 discloses a high-speed fluorescence scanner. The system utilizes a lightweight scan head to scan a collimated excitation beam across the sample. The emitted fluorescence is gathered by the scan head lens and directed back along the optical path of the excitation beam to a detector. In order to obtain a two-dimensional image of the sample, the sample is translated in an axis orthogonal to the scan line.
In a publication entitled Imaging as a Tool for Improving Length and Accuracy of Sequence Analysis in Automated Fluorescence-Based DNA Sequencing by Sanders et al, a method of signal analysis is disclosed. (Electrophoresis 1991, 12, 3-11). In the disclosed method, a computer program was used to remove distortions in the DNA bands in sequencing gels, thus improving the accuracy of DNA sequence analysis. The authors noted that the disclosed techniques should be applicable to other systems such as gel electrophoresis of proteins and DNA restriction fragments.
The scanners described above do not take full advantage of the wide range of different sample types available. Rather, a typical scanning device is designed for a specific type of sample, e.g., fluorescent samples, and as a result is incapable of use with another type of sample. In addition, many biological sample scanners offer a very limited set of irradiation/excitation wavelengths and/or emission wavelengths, thus further limiting the functionality of the device. Lastly, the resolution offered by many, if not all, of the fore-mentioned markers is not fully utilized by most biological sample scanning systems.
Therefore a compact optical scanner capable of use with a variety of sample types and configurations that offers multiple excitation/irradiation wavelengths and that may be used to detect emissions at a variety of wavelengths is desirable.